Elastic substantially linear ethlene polymers

Abstract

A continuous polymerization process of preparing ethylene polymers containing less than about 20 ppm aluminum, and having processability similar to highly branched low density polyethylene (LDPE), but the strength and toughness of linear low density polyethylene (LLDPE). The polymers have processing indices (PI's) less than or equal to 70 percent of those of a comparative linear ethylene polymer and a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a traditional linear ethylene polymer at about the same I 2 and M w /M n . The novel polymers can also have from about 0.01 to about 3 long chain branches/1000 total carbons and have higher low/zero shear viscosity and lower high shear viscosity than comparative linear ethylene polymers. The novel polymers can also be characterized as having a melt flow ratio, I 10 /I 2 , ≧5.63, a molecular weight distribution, M w /M n , defined by the equation: M w /M n ≦(I 10 /I 2 )-4.63, a critical shear stress at onset of gross melt fracture greater than about 4×10 6 dyne/cm 2 , and a single DSC melt peak between -30 C. and 150 C.

We claim: 
     
       1. A continuous polymerization process of preparing an ethylene polymer containing less than about 20 ppm aluminum, and having (i) a melt flow ratio, I 10  /I 2 , ≧5.63, (ii) a molecular weight distribution, M w  /M n , defined by the equation: M w  /M n  ≦(I 10  /I 2 )-4.63, (iii) an average of about 0.01 to about 3 long chain branches/1000 total carbons, and (iv) a critical shear stress at onset of gross melt fracture of greater than about 4×10 6  dyne/cm 2 , said process characterized by continuously contacting in a polymerization reactor a reactant selected from the group consisting of ethylene alone and ethylene and one or more C 3  -C 20  alpha-olefins, with a catalyst composition under continuous steady state polymerization conditions, wherein said catalyst composition is characterized as: (a) A metal coordination complex corresponding to the formula: ##STR8## wherein: M is a metal of group 3-10, or the Lanthanide series of the Periodic Table of the Elements;   R' each occurrence is independently selected from the group consisting of hydrogen, alkyl, aryl, silyl, germyl, cyano, halo and combinations thereof having up to 20 non-hydrogen atoms;   Z is a moiety comprising boron, or a member of group 14 of the Periodic Table of the Elements, and optionally sulfur or oxygen, said moiety having up to 20 non-hydrogen atoms;   X independently each occurrence is an anionic ligand group or neutral Lewis base ligand group having up to 30 non-hydrogen atoms;   n is 0, 1, 2, 3 or 4 and is 2 less than the valence of M; and   Y is an anionic or nonanionic ligand group bonded to Z and M comprising nitrogen, phosphorus, oxygen or sulfur and having up to 20 non-hydrogen atoms, optionally Y and Z together form a fused ring system, and   (b) an activating cocatalyst.   
     
     
       2. The process of claim 1 wherein the polymerization temperature is from 20 C to 250 C, wherein the ethylene concentration is from 6.7 to 12.5 percent by weight of the reactor contents, and wherein the concentration of the ethylene polymer is less than 5 percent by weight of the reactor contents. 
     
     
       3. The process of claim 2 wherein the ethylene concentration is further characterized as not more than 8 percent of the reactor contents to form an ethylene polymer having a I 10  /I 2  of at least about 8. 
     
     
       4. The process of claim 1 wherein (a) is an amidosilane or amidoalaediyl compound corresponding to the formula: ##STR9## wherein: M is titanium, zirconium or hafnium, bound in an eta 5  bonding mode to the cyclopentadienyl group; R' each occurrence is independently selected from the group consisting of hydrogen, silyl, alkyl, aryl and combinations thereof having up to 10 carbon or silicon atoms;   E is silicon or carbon;   X independently each occurrence is hydride, halo, alkyl, aryl, aryloxy or alkoxy of up to 10 carbons;   m is 1 or 2; and   n is 1 or 2.   
     
     
       5. The process of claim 1 or 4 in which component b) is an inert, noncoordinating boron cocatalyst. 
     
     
       6. The process of claim 1 or 4 in which the cocatalyst is trispentafluorophenyl)borane. 
     
     
       7. The process of claim 1 or 4 wherein the process is: (A) a gas phase process,   (B) a suspension process,   (C) a solution process, or   (D) a slurry process.   
     
     
       8. The process of claim 7 wherein the polymerization conditions comprise a reaction temperature and ethylene concentration sufficient to form an ethylene polymer having a I 10  /I 2  of at least about 8.